This invention is concerned with heat shields, for example heat shields for use in vehicles.
Many vehicles contain significant sources of heat from which it is necessary to shield heat sensitive equipment, cargo, or passengers. For example, passengers in an automobile may need to be shielded from heat generated by an exhaust system, or electrical or electronic components may need to be shielded from heat generated in an engine.
Heat shields used in vehicles must combine good resistance to heat transfer with acceptable acoustic properties, i.e they must not generate significant noise as the vehicle operates. Clearly, such heat shields must also be able to withstand the temperatures to which they are subjected in service. Other desirable properties are lightness, compactness, cheapness and suitability for recycling, i.e. use of readily re-usable materials is preferable especially use of a single such material.
Many heat shields have a substantially continuous heat-reflecting surface designed to reflect radiant heat back towards the heat source. Generally, such surfaces are provided by metal members which can withstand the temperatures experienced and are good reflectors of infra-red radiation. Aluminum or an alloy thereof can be used as it is a particularly good reflector of infra-red radiation and is lighter than, for example, steel. However, as metal is a good conductor of heat, it is necessary to provide such metal members with means for reducing thermal conduction therethrough. Such means may be provided by adding a material with good thermal insulating properties, for example mineral wool. Such material may, however, be expensive, increase the weight of the shield, and reduce its suitability for recycling. An alternative way providing thermal insulation is to create one or more enclosed or partially enclosed air spaces since air is a good thermal insulator. Such air spaces can be created between sheets of metal which are corrugated, or embossed, so that they make only limited contact with one another so that there are insulating air spaces between the contact areas. Such sheets have to be thick enough to have sufficient strength to retain their spacing, i.e. they have to be substantially rigid. Such constructions may, however, be unacceptable acoustically as ringing effects may occur and must have a substantial thickness to allow for the air spaces. An example of a prior art heat shield is described in U.S. Pat. No. 5,011,743 (Sheridan).
The present invention has the object of providing an improved heat shield with good resistance to heat transfer and good acoustic properties.